<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        canvas {
            border: 1px solid #ccc;
        }
    </style>
</head>
<body>
<canvas width="600" height="400"></canvas>
<script>
    var myCanvas = document.querySelector('canvas');
    var ctx = myCanvas.getContext('2d');


//    1.绘制坐标系
//    2.确定原点
//    3.确定距离画布旁边的距离
//    4.确定坐标轴的长度
//    5.确定箭头的大小  是个等腰三角形  10
//    6.绘制箭头填充

    var space = 20;
    var arrowSize = 10;

//    计算原点
    var canvasWidth = ctx.canvas.width;
    var canvasHeight = ctx.canvas.height;

    var x0 = space;
    var y0 = canvasHeight - space;

//    绘制x轴
    ctx.beginPath();
    ctx.moveTo(x0,y0);
    ctx.lineTo(canvasWidth - space,y0);
    ctx.lineTo(canvasWidth - space - arrowSize,y0 + arrowSize / 2);
    ctx.lineTo(canvasWidth - space - arrowSize,y0 - arrowSize / 2);
    ctx.lineTo(canvasWidth - space ,y0);
    ctx.fill();
    ctx.stroke();

//    绘制y轴
    ctx.beginPath();
    ctx.moveTo(x0,y0);
    ctx.lineTo(space,space);
//    箭头
    ctx.lineTo(space + arrowSize / 2, space + arrowSize);
    ctx.lineTo(space - arrowSize / 2, space + arrowSize);
    ctx.lineTo(space,space);
    ctx.fill();
    ctx.stroke();

</script>
</body>
</html>